mortarboard

American  

[mawr-ter-bawrd, -bohrd] / ˈmɔr tərˌbɔrd, -ˌboʊrd /

noun

1. a board, usually square, used by masons to hold mortar.

2. Also called cap.  a cap with a close-fitting crown surmounted by a stiff, flat, square piece from which a tassel hangs, worn as part of academic costume.

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mortarboard British  

/ ˈmɔːtəˌbɔːd /

noun

1. a black tasselled academic cap with a flat square top covered with cloth

2. Also called: hawk.  a small square board with a handle on the underside for carrying mortar

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Etymology

Origin of mortarboard

First recorded in 1850–55; mortar ² + board